This invention relates to measuring the thickness of a wall of a hollow vane.
One of the characteristics of these parts is that they are normally equipped with internal partitions covered by the wall, in order to stiffen the vane or divide the internal volume into compartments. These partitions interfere with measurements since their contributions to the measurement signal are superimposed with those of the wall and therefore they tend to be confused with additional thicknesses. Several non-destructive methods already exist that are liable to perform thickness measurements, but some, such as X-ray tomography where a detector network takes successive views around the object to be examined, are too complicated to use, while others, such as infrared measurements, are insufficiently accurate. Finally, ultrasound measurements are not suitable for all materials, particularly those which are anisotropic.
A particularly non-destructive thickness measurement method free of these shortcomings has been developed to give accurate and reliable indications on the thickness of a wall in spite of the presence of partitions behind said wall, at inaccurately known positions and which interfere with the thickness measurements.
The method is based on the use of a specific eddy current detector, which is designed and used such that the contribution of the partitions to the signal detected is minimised, and processing means are proposed to eliminate the influence of the partitions on the measurement substantially. Several specific embodiments are possible, which are more or less refined and give accurate results accordingly.
In its most general form, the invention relates to a method to measure the thickness of a hollow vane wall liable to cover partitions, characterised in that it consists of applying two poles of a magnetic code of an eddy current detector on the wall in parallel alignment with the partitions, the poles 8 being equipped with coils 7 connected to each other in series, moving the detector on the wall perpendicular to the partitions, recording a signal produced by the detector and deducing the thickness of the wall according to preliminary calibrations.
The document U.S. Pat. No. 4,005,359 A discloses an eddy current probe applied to estimate the thickness of a paint or enamel coating on a conductive substrate, it is composed of two windings arranged as a transformer, i.e. associated by electromagnetic induction but not connected electrically.
The document U.S. Pat. No. 5,172,059 A shows that a coil inducing eddy currents in a substrate under it is sensitive to variations in the thickness of said substrate.